DESCRIPTION To analyze complementary binding sites for the interaction of alpha-neurotoxins with the delta and gamma subunits of the pentameric nicotinic acetylcholine receptor (nAChR), the correlation of kinetic data for combination of mutations in both the receptor and the alpha-toxin are proposed. The snake venom toxin Naja mossambica mossambica (Nmm1), expressed from recombinant DNA bacterial systems, and mouse muscle nAChR, expressed transiently from the association and dissociation rates of the peptide Nmm1 toxin with the nAChR utilizing chemical labeling and site- specific mutagenesis, would critical structural determinants on both the toxin and the receptor responsible for binding recognition. The analysis of the binding energetics by a thermodynamic mutant cycle analysis should further characterize the orientation of the disulfide loops of the alpha- toxin with respect to the alphagamma and alphadelta interfaces on the nAChr. The long range goal of this proposal is to provide a comprehensive view of the alpha-neurotoxin-receptor complex by elucidation of the specific amino acid side chains involved in agonist and competitive antagonist binding interactions and to provide further insight as to the receptor's molecular architecture and mechanism of action. The nAChR is a ligand gated ion channel involved in fast synaptic communication and in initiating intracellular events. A detailed experimental model of the receptor's extracellular domain can be expanded to diverse members of this superfamily present in the central nervous system, which include receptors for acetylcholine, gamma-aminobutyric acid, glycine, and serotonin, with the hope that the molecular bases of cell signaling in the nervous system will be better understood.